The area of application extends principally to rail vehicles, the compressed-air supply system of which serves primarily to provide a brake pressure for the vehicle brakes. To produce braking air which is as dry as possible, the compressor-operated compressed-air supply system comprises an air drying unit for air preparation, the unit removing the moisture contained in the compressed air which has been drawn in from outside and compressed. For this purpose, single- and two-chamber air driers are the principal types used in the construction of rail vehicles, the driers removing the moisture from the compressed air and discharging it to the outside in condensate-laden compressed air.
DE 34 45 699 A1 has disclosed a single-chamber air drier which is provided for compressed-air supply systems that can be charged in intermittent mode and in which has a single regeneratable drying cartridge and a moisture sensor which measures the prevailing air humidity in the air reservoir volume. During the idling phase of the compressor with air humidity in the air reservoir which exceeds a defined threshold, an electronic evaluation unit initiates regeneration of the drying cartridge. During the regeneration mode, the compressed air is passed backward through the drying cartridge in such a way that the condensate-laden compressed air emerging from the cartridge reaches a discharge valve for discharge to the outside. The discharge valve is provided with an unenclosed exhaust port, with the result that the condensate-laden compressed air is released to the outside with a loud outflow noise. Owing to the switch to the regeneration mode, this outflow noise is preceded by a surge of compressed air, which can reach extreme noise levels. Especially in the case of rail vehicles parked in stations close to residential areas, this leads to noise pollution, especially when the rail vehicles are supposed to be held in readiness overnight.
DE 35 33 893 A1 discloses a two-chamber air drier in a compressed-air supply system for rail vehicles, which has two drying canisters which can be operated in alternation to ensure a continuous compressed air supply. While the compressed air flow produced by the compressor is being dried in one of the drying canisters, the desiccant in the other drying canister is regenerated. By means of a switching valve connected to the two drying canisters, compressed air to be dried is introduced into one of the drying canisters in an alternating sequence that can be predetermined in terms of time, and air used in each case during regeneration in the other drying canister is discharged from the latter. The switching valve furthermore has an outlet opening for discharging condensate-laden compressed air formed during the regeneration of the drying canister in the regeneration mode. Uncontained exhaust air passes to the outside from this outlet opening too.
An attempt has already been made to provide the outlet openings of known air drying units for rail vehicles with a sound suppressor, the latter generally being embodied as a sintered metal or plastic part or as a container filled with suppression material. However, solutions of this kind are of considerable size and achieve only limited sound suppression.
Known prior art sound suppressors furthermore have the disadvantage that the condensate contained in the compressed air freezes in the sound suppressor and can thereby obstruct the exit of the compressed air to the outside.